Restoring a special Ericsson type 1931 (DBH1001)

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This model is such a classic that it certainly merits a restoration report. It is one of the most influential telephones ever made. There are many versions, many derivatives and many models that were directly or indirectly inspired by it. See for more information on the Ericsson type 1931 (DBH1001) this article. 

Although this model is special in certain ways, it is basically the standard version. That makes it a good subject for this restoration report, so that many others may learn from it.

I got it several years ago. After I bought it, it turned out the surface bakelite was in very bad condition. It was rough and greyish white. It seemed as if there was some chalky residue on it, as if it had been immersed in water for a while. I tried to polish it by hand and with my dremel, but did not get it to shine properly. I marked it as a write off and kept it for spare parts.

Later I realized that a phone of this type with PGEM letters on the dial is very unusual. So I decided to put it away as a restoration project. As the bakelite was too bad to restore, I thought I would find a specimen with the same logo’s on the body shell and handset and combine the two to make a good one.

Trying out new techniques I found I could now give the bakelite an very acceptable shine, so it turned out I could restore this phone after all!

Something special

As said, this model also has some special characteristics. It was used by PGEM, the Provinciale Gelderse Energie Maatschappij (Province of Gelderland Energy Company), a state owned power company in the Netherlands, hence the letters PGEM on the dial centre.

These phone companies had their own telephone networks in their infrastructure, spanning the whole province. These phone networks were fully automatic from an early age. I have phones from some of the other energy companies, all marked with the acronym of their original owner.

This is the only one I have from PGEM and also the only one I have ever seen.

Aside from that it has an Ericsson logo on the top of the body shell and on the handset I have not seen very often. It is not super rare, but we do not see them very much here in the Netherlands. That is why I never found that replacement body shell.

Lastly there is another characteristic I find unusual: the dial has an extra number ring on the base plate. It is black with white numbers and usually it is bare nickel plated metal, with the numbers only on the center disc.

So a standard model with a number of interesting & uncommon details: a perfect candidate for an indepth and full restoration.

Preparations and taking stock

When I got this phone the bakelite had a very rough surface and before I started restoring it properly I experimented with polishing the body shell. So It was already partially polished when I started. The handset was not polished yet and the dial was very dirty. The nickel plated brass parts had a brownish tarnish together with some oxidation.

The cloth covered cords were frayed, with the outer mantle missing in some place. The line cord was cut, with little over 1 mtr left.

The feet were deformed and one had disappeared.

The mouth piece of the handset was missing, together with the transmitter cap. The receiver diaphragm was very rusty.

The inside was in good condition, although somewhat dirty. The frame had some rust, mostly under the paint.

I tested the electronics, without the dial and with a test handset and found them to be in proper working order.

The phone itself seemed to be largely original and untouched. I found no traces of conversion, refurbishment or major repairs. The only alteration I found was that the cord for the dial was changed to a newer, plastic covered one. The original would have been cloth covered, with different coloured wires.

Unfortunately the diagram was missing, the glue with which it was stuck on still visible.

Painted metal first….

I first removed the remains of the feet from the bottom plate. Then I removed the electronics from the metal frame. These were the 2 main black painted steel parts and I wanted to clean and polish them together.

I normally give the innards of a phone just a superficial clean and brush, especially if they are in good condition, apart from cleaning contacts and lightly oiling moving parts. In this case there was some rust on the metal frame, oxidation and tarnish on some screws and bare metal parts. I wanted a better look at some of the parts used, especially the capacitor.
And as I was cleaning and polishing some of the parts in any case and I wanted to avoid differences in finish between treated and untreaded parts it was really a choice of doing nothing or doing everything.

So I liberated the metal frame and remove the decayed feet, of which there were only 3 still remaining. Please note that I normally leave the feet in place. The rubber becomes vulnerable and brittle over time and there is a good chance they will damage if you remove them.

I gave these black metal painted parts a clean and polish with a special compound called Commandant no 4 for paints. Afterward I rubbed them with a little oil, giving them an even sheen/shine.

Cleaning the inside/electronics

I wanted to do these first following the treatment of the metal frame, as I wanted to put them back together again as soon as possible. The solid core wiring loom is vulnerable and prone to bending.

I lightly brushed most of the parts with a clean tooth brush. Please mind that the coils of the ringer are covered with some kind of thread, perhaps cotton. There were some white bits stuck to it, the size of grains of sand. Not sure what it was. Removed them carefully with a sharpened tooth pick, using a magnifying glass.

I also gave the capacitor a good clean and polish, making sure I avoided the lettering. I did not want to rub that off.
I polished the outside of the blades of the hookswitch with my dremel and polished the bracket that held the capacitor and the hookswitch mechanism with my buffing wheel to give them a high gloss.
I did more or less the same with the bells, buffing wheel for the outside, dremel for the inside.

I took some extra care to clean the bakelite block with terminal screws. It had some stubborn dust in places, I had to bend away some of the wiring to get at it, and the nooks and crannies around the terminals needed a good clean.

And of course I gave all the removed metal parts a good polish with my dremel. They were all nickel plated, screws mostly. Some had a little oxidation, which I pre-treated with some fine steel wool.

Dial: complete disassembly

Well, the dial needed a lot of work. The finger wheel had a coating of brown goo, some oxidation. The paint on the dial center was in bad schape. The metal number ring should have white numbers, but they were almost invisible.

Fortunately the dial mechanism is contained in a metal box, so it was reasonably clean and there was almost no oxidation.

So I cleaned and oiled all the mechanical parts. The nickel plated exterior parts I first treated with steel wool, to get the brown goo and most of the oxidation of. I polished them with chrome polish, using my dremel.

Afterwards I used my buffing wheel on them. This made them very shiny, but also the brass began to shine through. I am not sure if this was because the nickel plating was deteriorated or because the buffing wheel was too aggressive.
I assume the former, as the center disk had similar wear and the brass shining through too. Nevertheless next time I will avoid using the buffing wheel.

The number ring had much wear and some of the paint has worn away. I had never seen such a number ring on this type of dial before, so it was interesting to examine it.
The ring is made of brass and is painted black. The numbers are stamped in and were originally painted white. I decided to repaint them, because the original white paint was beyond restoration.
I filled the numbers in with white paint using a tooth pick. After an half hour of drying I wiped away the excess paint. I did this twice leaving the numbers looking nicely white and sharp.

The center disk I cleaned and polished it with Commandant no 4 for paints. The white lettering had some discolouration which seemed to be stuck on top of the white paint. I tried several methods to remove it, basically using a cleaning fluid, (water, glass cleaner, alcohol, white spirit) and a toothbrush and tooth pick, but the discolouration would not go away. I did not want to damage the letters, so I left them like this.
I also did some metal work: I hammered out a shallow dent, which slightly deformed the disk.

Reassembly was uneventful. I will calibrate and adjust the dial when the whole phone is finished.

I considered replacing the dial cord with an original cloth covered one, but I do not have a spare one. I may do this later.

Treating the bakelite

When I got this phone, it was the bakelite was very rough and greyish in appearance. It had been kept in a high moisture environment for quite a while, which also caused corrosion of metal parts too. Normally I would polish the bakelite with a felt polishing wheel on my Dremel and some polishing past. I had tested this method on a small part of the phone  long ago, but it did not give satisfactorily results. So I regarded it as a parts phone.
A while ago I acquired a small drill press. I had wanted one for quite a while now, because I could use it for other things besides drilling and it does not take as much space on my work bench as a benchgrinder/buffing wheel.

I tested polishing several pieces with a cloth polishing wheel I got and got remarkable results on this phone, much better than with my Dremel.

I used a fine polishing soap and pressed the bakelite quite hard against the wheel. It is important to get a firm grip on your work-piece, because it will fly across  the room if you lose grip, with devastating results, of course.

Please not that the buffing wheel does not get into the details of the raised and recessed Ericsson logos very good on the handset and body-shell. These I did with my Dremel and polishing agent.

Cords

I could write a whole article about what I did to the cords of this phone. I tried a new method on these too. I recovered them with black shoe laces.

This is a method I learned from my friend Jörg. Take a wide flat black shoe lace, the kind they use on sneakers and snip of the ends. The lace is a hollow tube which you can slide over the original inner wires.

I thought about replacing the cords. The problem is that the replacement cords I have have vinyl covered inner wires instead of cloth covered ones. And the original ones had these lovely original Ericsson eyelets with coloured ends. All in all this would be hard to replace.

The line cord was cut off at one end, making it easier to slide the new cloth covering over it. The handset cord was damaged where the cord entered the handset. The inner wires were broken at that point, the cord only held together with the cloth covering.

I removed all the old cloth covering, leaving the wire wrapping at the far end, to keep everything together.

I made a small hook at the end of a long thick aluminum wire and slid the new cover over the wire. Then I attached the hook to the end over the inner wires of the old cord with a piece of string and proceeded to slide and rub the new cover over the old cord.

I was very pleased with the result. It looked very much like the original wires and the cords were nice and souple.

After that I proceeded to make new eyelets where the cords were cut/damaged. I took one of the old eyelets apart by unwinding it, to get a good idea how they were made.
I removed part of the cloth cover of the inner wires and held a small piece of copper thread along the exposes wires. I twisted everything together and wound the rest of the copper wire around it. I bend the wound end into an eyelet and wound coloured yarn around  it, to keep the eyelet together.

The ends of the cords were wound with coloured yarn, for which I found reasonably close replacement. So I rewound the ends of the cords, to match the original. I even reused the original strain relief for the handset.

Reassembly

Reassembly was pretty straight forward. I took lots of pictures before and during the disassemble process. I also test fitted most replacement parts at the beginning of the restoration process.

I had not tested the handset, and more specifically the transmitter and receiver. The transmitter had a lot of corrosion, but after clean up and polish it worked quite well. I removed most of the corrosion with fine steel wool. Afterwards I gave it a polish with my buffing wheel.

I also had not tested the dial yet and the wires of the dial were disconnected long ago. As I had no diagram I had to do some reverse engineering and research on diagrams of similar models to properly connect it. Fortunately I got the dial and with that the whole phone working.

Final touch: connectivity and label

How am I going to connect this phone? This is a question I find very important. I like to do justice to the history and originality of the phone, so something from the period where this phone has my preference. I am not sure what was on the end of the line cord. This model basically came in 2 version: with a terminal box or a three pronged plug.
PGEM may have used non-standard terminal boxes or plugs, but I do not have any information on that. So it is purely a guess on my part about what was at the end of the line cord.
I wanted to put on a standard Ericsson terminal box and I found a really nice one in my stash of terminal boxes. Unfortunately it had Dutch markings on the bakelite base where the phone itself was made in Sweden. This bothered me, so I opted for a plug instead.

Another thing I find importand is to put a proper paper label on a telephone. In this case I no longer had an original number card or clear plastic covering for it.
I did not want to put a paper in it with some kind of fantasy period number. So I made a label with a white Ericsson logo on a black background. Ericsson used to put similar labels on their phones, back in the day. It took some careful measuring to get the size right. I did put an older clear plastic piece over it. It was a bit yellow, so looked quite old. Just the thing for this phone. It is the cherry on the apple sauce, as we say in the Netherlands.

Calibration and adjustment

After reassembly and connecting it up everything worked properly. The telephone received, transmitter, could make outgoing calls (at least on my test exchange) and the ringer worked properly too.

Of course I adjusted the bells. It is something I always do, to make sure they give a nice chime.

The final thing I wanted to check was the working of the dial. Because it had been completely disassembled the performance may be off. Most important is the correct number of pulses per second (pps). Too fast or too slow, and the exchange will not respond to the dial. 10 pps is the norm, but most exchanges are tolerant between 8 to 13 pps. I usually adjust a dial to 11 pps, as it will slow down a with the passing of time.

The other thing that is important is the ratio between the pulses and pauses. In other words the ratio between the pulse contact on and the pulse contact off. This should be around 15%. Modern exchanges that accept pulse dialing are quite forgiving as are pulse to tone converters, but old electro mechanical exchanges are sensitive with regards to this.

Also a fellow collector has been asking me several times about this with regards to this particular dial design, so all the more reason to document what I did and share my experiences.

So I whipped out my telephone tester and measured the pps and pulse ratio(?) and made videos about the result.

It turned out that the pps were a little high: almost 14. So I had to adjust the gouvernor a little. Make/break ratio was about 35% which was perfect.

The result

It is not often that I restore a phone down to the very last screw. This phone really needed it. I even tried several new techniques on it: polishing with a buffing wheel instead of a Dremel., recovering old cords with a shoe string, making new eyelets.

I have seen shinier bakelite, after polishing. But this is the best result I could get at the moment. And I must say it has come a long way

I am very pleased how this phone turned out. I was able to use and reuse all the original parts, except the feet.

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